The present invention relates to a shear.
Known are shears for transversely cutting a steel or the like strip moving horizontally and longitudinally.
For example, Japanese Patent 2nd Publication No. 61-53172 discloses a drum shear comprising upper and lower drums rotatably extending transversely of a strip. Each of the drums has a blade fixed thereto and extending transversely of the strip. The drums are mechanically interlinked through a transmission such as gearing so as to be synchronously driven.
Japanese Patent 1st Publication No. 52-132485 discloses a drum flying shear comprising upper and lower drums rotatably extending transversely of a strip. Each of the drums has a blade fixed thereto and extending transversely of the strip. Either or both of the drums are vertically movable for retraction of the corresponding blade or blades away from the strip feed line.
FIG. 1 shows a conventional shear in which, in a shearing operation, drums a and b are energized such that the strip e is moved at a running velocity V at a center X of a lap between the blades c and d.
FIG. 2 represents another conventional shear which comprises a housing f having vertically movable upper and lower drum chocks i and j therein for rotatably supporting upper and lower drums g and h. The upper drum chock i is vertically movably connected through an eccentric wheel 1 and a connecting rod m to a rotary shaft k rotatably supported by the housing f whereas the lower drum chock j is vertically movably supported through a vertically extending cylinder n to the housing f. Reference numeral o represents a balance cylinder between the drum chocks i and j.
In a shearing operation, the upper and lower drums g and h which have been stopped are synchronously rotated. At the same time, the rotary shaft k is rotated to vertically move the upper drum chock i through the wheel 1 and the rod m. When the rotating velocity of the drums g and h becomes equal to the strip feed velocity and the upper drum chock i is lowered, the cylinder n is extended and the lower drum chock j is moved up so that the strip is cut off between the drums g and h.
According to the drum shear in the Japanese Patent 2nd Publication No. 61-53172, the upper and lower blades cut off the strip before the drums are rotated by one turn. Therefore, the drums cannot be accelerated from the stopping state to full extent, failing to move the strip at high velocity.
In the drum shear of the Japanese Patent 1st Publication No. 52-132485, the upper and lower drums are not mechanically interconnected through a transmission so that it is difficult in a shearing operation by rotating the upper and lower drums to maintain constant a gap between the upper and lower blades, failing to neatly cut the strip.
In the conventional shear as shown in FIG. 1 with the strip e running at a running velocity V, a velocity V' of the blades c and d in contact with the strip e as shown in one-dot chain line in FIG. 1. is: EQU V'=V cos .theta.
and is slower than the running velocity of the strip e. As the result, scratches may be produced on surfaces of the strip e by edges of the blades c and d due to such velocity difference. This is undesirable in terms of production yield.
With the conventional shear shown in FIG. 2, the upper and the lower drums g and h are vertically moved by separate drive means. That is, two series of drive systems are required. It is very difficult to synchronize the vertical movements of the drums g and h by the two drive systems.